One of the biggest complaints about traditional hot tubs made from fiberglass and acrylic is that they fade, peel and crack. Cracking leads to leaking and you can imagine the damage a cracked rooftop hot tub would create.
All of Diamond Spas products are made from stainless steel and copper. Steel and copper are ductile materials. They can bend without breaking. These metals can withstand tremendous force prior to deforming or throughout deformation to an eventual failure, or "cracking". These metals will crack if you can apply enough force to bend it far enough, but you aren't going to break a stainless steel spa with a hammer, which is also made of steel.
The failure of any material occurs at the weakest point of quality control in terms of design, manufacturing, and assembly or construction. We purchase mill certified stainless steel, assemble under controlled conditions, and then test the product prior to delivery. So we're confident our products aren't going to crack.
If you do so see an instance where steel has "cracked" it's probably at a weld joint, the weakest point of quality control for that product, or it wasn't designed properly, or an excessive force was applied to an otherwise suitable design.